Currently, most digital cameras use a zoom lens and a single color image sensor to capture still and motion images. The captured images are then processed to produce digital image files, which are stored in a digital memory in the camera. The digital image files can then be transferred to a computer, displayed, printed, and shared via the Internet. The motion image sequences captured by these digital cameras are typically compressed, for example by using the well-known MPEG-4 compression standard, and the compressed data is stored using solid-state or magnetic memory.
To provide a motion image sequence having fluid motion, the exposure time of the sensor used to capture the image needs to be sufficiently long (relative to the frame rate) in order to avoid temporal aliasing. If the exposure time is too short, motion artifacts (such as backward-turning wheels on forward-moving cars) may appear in the captured motion image sequence. However, in order to obtain sharp digital images of moving subjects, such as is required to produce a good still image from one of the motion frames, the exposure time must be short enough to freeze the subject. Thus, there are conflicting requirements between minimizing temporal aliasing and providing sharp “freeze frame” images.
To provide a small size digital camera with a large “optical zoom range”, the digital camera can use multiple image sensors with different focal length lenses, as described in commonly assigned U.S. Publication No. 2006/0187312 entitled “Digital Camera Using Multiple Lenses and Image Sensors To Provide an Extended Zoom Range”. For example, the Kodak Easyshare V610 dual lens digital camera includes a 38-114 mm (35 mm equiv.) f/3.9-f/4.4 lens and a 130-380 mm (35 mm equiv.) f/4.8 lens, in order to provide a 10× optical zoom range. However, in both this above-referenced patent application and product, only one of the two image sensors is used at a time. The two image sensors cannot simultaneously capture motion images.
U.S. Publication No. 2003/0020814 dated Jan. 30, 2003 to Ono discloses a camera having two different lenses which are coupled to two CCD image sensors. In the various embodiments described in this disclosure, the two lenses can provide different focal lengths ranges, or they can be fixed focus lenses set to two different focus distance settings. However, the two image sensors cannot simultaneously capture motion images.
Some video cameras use multiple image sensors to form a color image. In most cameras of this type, a single lens is used to provide an image of the scene, which is then separated into multiple colors by a prism beam splitter. Multiple monochrome image sensors are used to capture red, green, and blue color separation images. However, as disclosed in U.S. Pat. No. 6,611,289, entitled “Digital Cameras Using Multiple Sensors with Multiple Lenses” and issued Aug. 26, 2003 to Yu et al., it is possible to use multiple image sensors and multiple lenses to provide color separation. But in both types of systems, all of the image sensors provide the same temporal sampling, in order to simultaneously capture the different color components of the image.
Some digital imaging systems also use multiple image sensors and multiple lenses to capture different portions of the digital image. Such a system is disclosed in U.S. Pat. No. 7,009,638 issued Mar. 7, 2006 to Gruber et al. In one embodiment disclosed in this patent, a large format digital camera exposes multiple detector arrays using multiple lens systems to acquire sub-images of overlapping sub-areas of large area objects. The sub-images are stitched together to form a large format digital macro-image. Again, all of the image sensors provide the same temporal sampling to simultaneously capture the different sub-areas of the image.
Stereo film cameras and stereo electronic cameras are known in the prior art. These cameras typically have two horizontally separated lenses of the same focal length, which focus two slightly different images of the scene onto two image sensors or two frames of film. Such a system is disclosed in commonly assigned U.S. Pat. No. 4,989,078, entitled “Still Video Camera for Recording Stereo Images on a Video Disk” and issued on Jan. 21, 1991 to K. Bradley Paxton. The two images provide a so-called “stereo pair”, which simulates the slightly different perspectives that a person's left and right eyes would see when viewing the scene. Again, both of the image sensors provide the same temporal sampling to simultaneously capture the stereo image pair.
Film cameras that use multiple lenses to capture multiple images at approximately the same time are also known in the prior art. For example, some cameras provide a shutter delay to expose different parts of the film at different times. Such a system is disclosed in commonly assigned U.S. Pat. No. 3,202,069, entitled “Sequence Camera” and issued on Aug. 24, 1965 to James B. Cummings and Theodore R. Kolter. A plurality of sequential still photographs is taken, each exposing a predetermined area of the film. The camera, however, is unable to simultaneously capture motion images.
None of these prior art systems address the conflicting requirements between minimizing temporal aliasing and providing sharp “freeze frame” images.
What is therefore needed is a digital camera that uses multiple image sensors to capture images of the same scene using different exposure periods.